Intraocular lens for patients with retinal degeneration

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INTRAOCULAR LENS FOR PATIENTS WITH RETINAL DEGENERATION

ערשה תוך עינית עבור תולים בעלי רשתית מרכזית מנוונת

P3219

DESCRIPTION

INTRAOCULAR LENS FOR PATIENTS WITH CENTRAL RETINAL DEGENERATION BACKGROUND OF THE INVENTION ₅ TECHNICAL FIELD

The invention relates to an intraocular lens for use in combination with an external lens system to form an image on the retina.

BACKGROUND ART one of the leading causes of blindness in America is macular degeneration. In this condition, the central retina, which perceives fine detail, is deficient. In the less severe cases of this disease, patients can often be helped by simple magnifiers or by 15 various telescopes, both of which serve to enlarge the image formed on the retina.

Magnifiers are used for reading or other tasks involving near vision. A variety of magnifiers are available and are generally useful for their intended 20 purpose. However, such magnifiers are bultiy and inconvenient and are of no help in other tasks such as walking about. Such magnifiers are likewise tiring to the user, thus detracting from their usefulness.

For improved distant vision, a telescope is 25 required. In order to be suitable for low vision patients, telescopes must be compact, light weight, and reasonably inexpensive. These requirements together with basic optical limitations generally result in a device which magnifies but with an enormous loss of 3C visual field. For the low vision patient, with his natural lens, telescopes of 2.2 X, 2.5 X, or 3 X are often prescribed for use outdoors, or for other distance viewing. The field loss is so great that most patients with macular degeneration de not find 35 telescopes of much practical value. Such telescopes are, therefore, often of limited practical use because

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P3219 - 2 of their narrow field, poor cosmetic appearance and difficulty in fitting to the patients face. As a result, they are used relatively infrequently by patients.

When patients have cataracts in addition to macular degeneration, the prognosis is even worse. Removal of the cataract, followed by vision correction with spectacles or contact lenses, renders the field of vision smaller without significantly improving 10 magnification.

The aphakic patient with a normal retina faces a formidable optical problem. Spectacle lenses of +11 +16 diopters are needed to provide the required additional focusing power. Alternatively, contact 15 lenses of similar power may be worn. For those who cannot wear contact lenses and must, therefore, wear spectacles, the lenses are thick and must be precisely fitted to the patient's face. Furthermore, the field of view is restricted by the refracting effect of the 20 lenses. Alternatively, contact lenses of similar power may be worn. However, a substantial number of patients, particularly older patients with limited finger dexterity, cannot wear contact lenses.

If the aphakic patient further has macular 25 degeneration, the conventional telescopic low-vision aids mounted on the spectacle frame will be a problem. The telescope adds weight, and projects beyond the already large spectacle lenses. The telescope further limits the field of vision. The field problem is 30 aggravated by the fact that the presence of the spectacle lens moves the telescope yet further from the eye than the optimum position.

Some aphakic low-vision patients can use a 6X or 8X hand-held telescope. The 6X has a field of view of 35 11., while the 8X has a field of 8. Yet, this solution is not viable ::or the many patients who do not

P3219 - 3 have the steadiness of hand to use such hand-held telescopes.

As a result of the above optical problems apd the already reduced visual acuity, low-vision patients who 5 develop cataracts are often not operated on.

Conversely, in other instances demagnification of the optical image is desirable. Thus, patients with retinitus pigmentosa (RP) and some patients with advanced glaucoma suffer a loss of peripheral vision. 10 In order to function normally, e.g., to cross the street, they may benefit from a visual aid that demagnifies the retinal image, thus putting more of the visual field onto the central portion of the retina that is still functional.

The principle of the invention and the various embodiments disclosed herein overcome the above deficiencies while achieving the objectives set forth.

A search of the prior art has uncovered the following materials:

TROUTMAN/ in an article entitled Artiphakia and

Aniseikonia, which appeared in the American Journal of Ophthalmology, pages 602-639, October, 1963, discusses the state of the art in artificial intraocular leases. On page 614, the article states: There is no reference 25 in the literature on intra-ocular lenses as to the telescopic magnification which can be attained with the combination of an intraocular lens and a spectacle lens.

LEVY, Jr. et al., U.S. Patent 4,074,368, disclose 30 an intraocular lens that is based on the principle of a Galilean telescope wherein both the negative element 18 and the positive element 14 are fastened together, and both placed within the eye. Positive element 14 is an air lens formed by bubble 15, and negative element 18 35 is an air lens formed by bubbles 20 and 22. The patent suggests implantation of this intraocular lens system

P3219 ⁴ ־ ' for relief of conditions such as macular degeneration and diabetic retinopathy.

LIEB, U.S. Patent 2,834,023, discloses anterior chamber lenses for refractive correction of aphakia, high ametropia, and anisometropia, and bilateral and unilateral cataracts. Of particular interest are Figs. 6-9, wherein lens 20 is of the diverging type.

FILDERMAN, U.S. Patent 3,027,803, discloses a spectacle lens-contact lens system which forms a modified Galilean telescope. Contact lens 10 serves as the negative lens in the telescope lens system, and central segment L2 of spectacle lens Ll serves as the positive objective lens of the telescopic lens system. Furthermore, the patent discloses how a 2X magnification system can be developed by using a negative lens of -50 diopters and a positive lens of +25 diopters.

DITTMER, U.S. Patent 2,164,801, discloses a corrective lens system wherein an alternate embodiment provides a telescopic lens system, as illustrated m Fig. 5. The telescopic lens system comprises negative contact lens 23 which is worn on eye 10, and positive spectacle lens 24 which is mounted in front of eye 10.

SPERO, U.S. Patent 2,078,590, discloses telescopic spectacles wherein positive lens 15 is secured to glass carrier member 16, and negative lens 17 is secured to second glass member 18. The total lens system is secured to a spectacle lens mounting system.

ISEN, in Feinbloom Mini-Scope Contact Lens as reported in the Encyclopedia of Contact Lens Practice (November 15, 1961), teaches making a Galilean lens system out of a doublet constructed contact lens. As can be seen, the negative lens is placed closest to the eye, while the positive objective lens is placed a small distance avay from the eye.

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P3219 - 5 DISCLOSURE OF THE INVENTION

It is an object of the invention to overcome the above disadvantages associated with conventional devices and techniques, and to provide a system 5 allowing for improved vision with a greater field of vision than was previously possible.

It is a further object of the invention to provide an optical system which is useful for improving distant vision by patients having macular degeneration and 10 aphakic patients and which is more acceptable cosmetically than are the presently available telescopic spectacles.

It is yet a further object of the invention to provide a system providing a demagnified retinal image 15 thereby placing more of the visual field onto the central portion of the retina thus aiding patients suffering from loss of peripheral vision.

According to one embodiment of the invention, a negative-power intraocular lens is provided which is 20 adapted to be’positioned in the posterior chamber of the eye. The intraocular lens is configured so as to provide an enlarged retinal image and a large field of vision when used in combination with an exterior positive lens.

According to one preferred embodiment of the invention, the exterior lens is a spectacle lens, while in another embodiment the external lens is a positive contact lens.

A second external lens may also be provided. In 30 this instance, the first external lens is a positive spectacle lens and the second external lens is a negative or a positive contact lens.

f According to the invention, a method for providing improved magnification to . ::: eyes having no natural 35 lens is disclosed. The method comprises implanting a negative intraocular lens within the eye; and providing

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P3219 - 6 an external positive lens. A second external lens may be used, in which case the first external lens is a positive.spectacle lens, and the second external lens is a negative or a positive contact lens.

According to a second aspect of the invention, the intraocular lens has a positive power while the external lens has a negative power. Such a combination provides a system which demagnifies the image to the retina while providing an improved field of vision.

Once again, the external lens can be a lens system comprising two lenses; i.e., a spectacle and contact lens.

In the corresponding method, a positive IOL is implanted in an eye and is combined with an external 15. negative lens so as to provide a demagnified image on the retina with an increased field of vision.

brief description of drawings

Fig. 1 is a cross-sectional view of one embodiment of an optical system of the invention,

Figs. 2k and 2B are front and side magnified cross-sectional views of the negative intraocular lens shown in Fig. 1,

Figs. 3A and 3B illustrate cross-sectional views of the intraocular lens inserted in the posterior chamber;

Fig. 4 is a graph comparing the magnification and field of vision of various optical systems, including the system of the invention;

Fig. 5 is a graph used for selecting the correct 30 intraocular lens, depending upon the magnification desired;

Fig. 6 is a diagram illustrating the field of view obtained through a spectacle lens.

Fig. 7 is an alts!native embodiment to the 35 embodiment shown in liga.e 1 for demagnifying the visual image.

P3219

BEST MODE FOR CARRYING OUT THE INVENTION

As was noted above, most broadly, the optical system of the invention includes an intraocular lens, such as is illustrated in Figs. 1 and 2 (or Fig. 7). Referring to Fig. 1, the negative power of the intraocular lens is selected sue.: that, when a spectacle lens or contact lens of appropriate power is worn, the patient will have a magnified retinal image.

As was noted previously, the intraocular lens may be used in combination with either a contact lens and/or a spectacle lens. When combined with a spectacle or contact lens of a positive power, the combination will behave as a Galilean telescope with a magnification factor greater than unity.

As seen from Fig. 1, a spectacle lens 7 having a positive refracting power is worn in combination with the negative intraocular lens 9 so as to focus the image on the retina 11. The intraocular lens is positioned behind the iris. It is also possible, although far less preferable, to position the lens in the anterior portion of the eye, between the cornea and the iris.

It is an advantage of the invention that the intraocular lens is positioned close to the pupil of the eye, thereby permitting the lens to be of relatively small size, as compared, for example, with negative-power contact or spectacle lenses which might otherwise be used for the same purpose. Additionally, by positioning the lens in the posterior chamber, maximum separation is achieved between the spectacle or contact lens used and the intraocular lens, thereby achieving maximum magnification.

The distance, v, shown in Figure 1 is the vertex distance, defined as the separation between the vertex of the cornea and the vertex of the spectacle lens. As will be explained below this distance is important in

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determining the magnification that is achieved.

The general intraocular lens structure contemplated is of the type which is generally known, such as, for example, the type disclosed in United 5 States Patent 4,041,552 to GANIAS, the disclosure of which is hereby incorporated by reference.

As may be seen from Figs. 2A and 2B, the intraocular lens is provided with loops or haptics 13 of plastic or metal for holding the lens element 15 10 firmly in position. Fig. 2b illustrates relative dimensions in millimeters. The clear aperture (CA) in this example is 4.5 mm.

Fig. 3A shows one possible technique for positioning the lens in the posterior chamber of the 15 eye. As illustrated, the haptics 13 expand by spring tension, contacting the inside surface of the capsule 15. In Figure 3B, the situation is illustrated in which the capsule has been removed, as in an intracapsular extraction. In this case the loops 13 20 expand against the ciliary body 17 and thereby position the IOL. The loops are shown as being inclined with respect to the plane of the IOL, the purpose being to position the IOL in a posterior position thus providing added separation between the IOL and the exterior lens. 25 The decision as to the type of IOL to use may be made at the time of surgery.

Naturally, in this embodiment, the intraocular lens and the spectacle and/or contact lens must be appropriately selected so as to provide the desired 30 degree of magnification, and a sharply focused retinal image, while providing optimal field of vision.

The power, P, of the IOL can be calculated from the equation:

p ־־ n nv + a 'l-vC) -FM g-b r.v” + b(l-vC)

P3219 where η = index of refraction of the intraocular media ^e 1.336 g = distance from cornea vertex to the retina (Fig. 1) in meters (m).

b = distance from cornea vertex to the IOL (m) v ־־ vertex distance of spectacle lens (m)

C = power of cornea, in diopters

F = focal length of normal (phakic) eye M = magnification desired once the power of the IOL has been determined from Equation 1, the power, S, of the spectacle lens can be found as follows!

S = - P(g-b) (n-bC) ־ n(n-gC)_______

P(g-b) (vbC-b-nv) + n(nv +g־vgC)

S is the power required for distant vision. If correction is needed for near vision, appropriate additional power can be added to S.

The field of view is defined with the help of Fig. 6. The total angular field is defined as the angle a .

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where d = diameter of spectacle lens (m) v = vertex distance from spectacle lens to the cornea (m) k ־־ distance from cornea vertex to nodal point of the eye (m). For the normal eye k = .007m.

S = power of spectacle lens, in diopters.

Practically speaking, the procedure for selection of the appropriate lenses may be as follows. The

P3219 patient’s requirements for magnification and field of view are determined from a detailed examination, including visual acuity, if possible, and from determination of the patient’s visual needs, e.g., distance vision vs. reading. From the available negative IOLs, the power that best meets the patient's requirements is selected. A graph such as that illustrated in Figure 4 may be used for this purpose. The intraocular lens will have a power of -10 to -100 diopters with lenses of -40 diopters to -100 diopters being very suitable. After the implant surgery, when the eye has stabilized sufficiently, the patient is refracted to determine the best spectacle ( or contact lens ) for optimum vision.

The spectacle lens can be of the conventional glass or plastic type. It is also possible to use a positive Fresnel lens in some cases, in order to reduce the weight of the spectacle. These lenses consist of thin plastic on which circular sections of a lens have been embossed. The finished piece acts as a lens, but the total thickness is much less than the conventional lens. They are especially useful in situations requiring large positive (or negative) dioptic powers.

Fig. 4 illustrates the magnification and field of view obtainable for the various IOL powers indicated in parentheses. For purposes of illustration, a fixed diameter of spectacle lens, 40 mm, was assumed. If a smaller diameter spectacle lens, or a spectacle Lens that is not round is used, the field will be different from that shown. Also illustrated in fig. 4 are the magnification and field obtainable in a number of currently available telescopic low vision aids, such as the bioptic, and the designs for vision wide angle telescope. It is apparent that for any given magnification up to 2.5 X, the combination of IOL plus spectacle lens yields a wider field of view than the

P3219 conventional telescopic low vision aids.

Curve B in fig. 4 illustrates the magnification and field obtainable with the combination of a contact lens and a spectacle lens. Since it is impractical to 5 utilize contact lenses of extreme negative power, the curve is extended only to -30 D. Curve B indicates that the magnification obtainable with this combination is quite limited. Comparison with curve A shows that for a given magnification, the field obtainable with 10 the lOL/spectacle combination is superior to that of the CL/spectacle combination.

Figure 5 is a graphical representation of the relation between IOL power and magnification for various combinations of IOL and external lenses. Line 15 A gives the magnification as a function of IOL power for the combination of an IOL and a spectacle lens located at a vertex distance of 13 mm (v = .013 m) from the cornea. This vertex distance is typical for many patients. Each figure in parenthesis is the required 20 power of the External lens, the spectacle lens in this case. Line B is for the combination of an IOL together with a contact lens. It is apparent that this combination does not offer the degree of magnification that can be obtained with the IOL/s pe c tac 1 e 25 combination. The reason is that the IOL and the CL are of necessity in fairly close proximity, as dictated by the anatomy of the eye.

Line C is for the more complex combination of an IOL, a contact lens of -20 D power, and a spectacle 30 lens. This arrangement increases the magnification available compared to either of the above combinations. The price to be paid for this additional magnification is the inconvenience of wearing a contact lens as well as a spectacle lens, and the increased power necessary 35 in the spectacle lens.

Line D represents the lOL/spectacle combination

P3219 - 12 with a vertex distance of 23 mm for the spectacle. This additional 10 mm of vertex distance is seen to give a significant increase in magnification compared to line A. There are two implications to this 5 observation. First, a given magnification can be achieved with a lower power IOL and lower power spectacle lens if the vertex distance can be somewhat greater than the standard 13 mm. Second, and perhaps more important, after an IOL has been in place for a 10 few years, the patient may require increased magnification, due to progressive macular degeneration. Rather than risk a second operation to replace the IOL, the patient can be fitted with spectacles having a greater vertex distance. For example, if the IOL were 15 a -60 D lens, the initial magnification for a vertex distance of 13 mm would be 1.97 X־. Later the magnification could be increased to 2.5 X by increasing the vertex distance to 23 mm, together with an appropriate change in the power of the spectacle lens. 20 While an increase in vertex distance does create minor problems in fitting spectacle lenses and in cosmetic appearance, the disadvantages are less objectionable than the traditional telescopic spectacles or hand-held telescopes.

As seen from the information provided by the graphs, the system of the invention provides improved magnification and increased field of vision over systems which are commonly available, while being easier to use and being far more cosmetically 30 acceptable. As was noted previously, it is a significant advantage of the invention that, for a given magnification, the intraocular lens-spectacle combination provides a larger field of view than any of the alternatives shown in Fig. 4.

Additional advantages cf the inventive combination are lighter weight, ־.nd fewer optical elements to be

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P3219 - 13 maintained in alignment. Cosmetically, a simple lens in front of the eye, even a strong positive lens, is less objectionable than a telescope mounted on the spectacle frame, as is presently employed.

The advantages of a system providing a wide field of view are obvious. A wide field greatly increases the ability of the patient to move about, to avoid obstacles, and generally to function normally, and, therefore, provides a viable alternative to systems 10 which have been proposed previously.

As has been noted above, the intraocular lens may be used in combination with a contact lens instead of a spectacle lens. The negative intraocular lens and positive contact lens once again act to form a Galilean 15 telescope. However, this embodiment is less preferred by virtue of the shorter spacing between the two lenses, as compared with the spacing between the intraocular lens and a spectacle lens. The magnification which is obtained is, therefore, quite 20 limited and 'fixed, as a result of the anatomy of the eye.

In yet another embodiment of the invention, a negative contact lens may be used in combination with a negative intraocular lens and a positive spectacle lens 25 to satisfy the parameters set forth previously. However, by virtue of the extra problems associated with contact lens wear, as well as the additional problems of alignment of the three lenses, this system is likewise less preferable than the simple intraocular 30 lens - spectacle lens system.

An additional embodiment of the invention employs a positive contact lens in combination with a positive spectacle lens and a negative intraocular lens. By dividing the reuqired positive power between the 35 spectacle lens and the contact lens, the power of the spectacle lens can be reduced, thus reducing its weight

P3219 and improving the cosmetic appearance. Furthermore, for a given magnification, the field of view is somewhat greater for the combination including the positive contact lens than for the spectacle/IOL combination.

Figure 7 illustrates an alternative embodiment of the invention which is useful with patients suffering from reduced peripheral vision. In this embodiment, the IOL and external lens powers are reversed such that the IOL 9’ has a positive power while the external lens 7' has a negative power. A graph similar to that shown in Figure 5 may be used for selecting various lens powers after the patient's visual requirements have been evaluated. By way of example, in this embodiment an IOL having a power of 40D in combination with a spectacle lens of -25D power at a vertex distance of 23mm gives a magnification of 0.59.

Although the invention has been described with respect to particular materials, lenses, and intraocular lens systems, it is to be understood that the invention is not limited to the particulars disclosed, but extends to all equivalents falling within the scope of the claims.